Implement EmptyResponse class

docs/responses.md

@@ -182,6 +182,29 @@ async def app(scope, receive, send):
     await response(scope, receive, send)
 ```
 
+### EmptyResponse
+
+Supplies an empty message body as the response.  
+
+In particular, use an EmptyResponse object for 1xx, 204, 205, 304 responses as it sets or omits a Content-Length header as appropriate.
+
+Signature: `Response(status_code:int, headers: typing.Optional[typing.Dict[str, str]] = None, background: typing.Optional[BackgroundTask] = None)`
+
+* `status_code` - An integer HTTP status code.
+* `headers` - A dictionary of strings.
+* `background` - A BackgroundTask to be executed when the response is sent.
+
+
+```python
+from starlette.responses import EmptyResponse
+
+
+async def app(scope, receive, send):
+    assert scope['type'] == 'http'
+    response = EmptyResponse(status_code=204)
+    await response(scope, receive, send)
+```
+
 ## Third party middleware
 
 ### [SSEResponse(EventSourceResponse)](/~https://github.com/sysid/sse-starlette)

starlette/responses.py

@@ -311,3 +311,51 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
                     )
         if self.background is not None:
             await self.background()
+
+
+class EmptyResponse(Response):
+    """Response to be sent with status code 1xx, 204, 205, 304, or whenever
+    an empty response is intended."""
+
+    def __init__(
+        self,
+        status_code: int,
+        headers: typing.Optional[typing.Dict[str, str]] = None,
+        background: typing.Optional[BackgroundTask] = None,
+    ) -> None:
+        super().__init__(
+            content=b"", status_code=status_code, headers=headers, background=background
+        )
+
+    def init_headers(self, headers: typing.Mapping[str, str] = None) -> None:
+        byte_headers: typing.Dict[bytes, bytes] = (
+            {
+                k.lower().encode("latin-1"): v.encode("latin-1")
+                for k, v in headers.items()
+            }
+            if headers
+            else {}
+        )
+
+        if self.status_code < 200 or self.status_code == 204:
+            # Response must not have a content-length header. See
+            # https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.2
+            if b"content-length" in byte_headers:
+                del byte_headers[b"content-length"]
+        elif self.status_code == 205:
+            # Response can either have a content-length header or a
+            # transfer-encoding: chunked header.
+            # We choose to ensure a content-length header.
+            # https://datatracker.ietf.org/doc/html/rfc7231#section-6.3.6
+            byte_headers[b"content-length"] = b"0"
+        elif self.status_code == 304:
+            # A 304 Not Modfied response may contain a content-length header
+            # whose value is the length of
+            # message that would have been sent in a 200 OK response.
+            # So we leave the headers as is.
+            # https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.2
+            pass
+        else:
+            byte_headers[b"content-length"] = b"0"
+
+        self.raw_headers = [(k, v) for k, v in byte_headers.items()]

tests/test_responses.py

@@ -7,6 +7,7 @@
 from starlette.background import BackgroundTask
 from starlette.requests import Request
 from starlette.responses import (
+    EmptyResponse,
     FileResponse,
     JSONResponse,
     RedirectResponse,
@@ -309,3 +310,34 @@ def test_head_method(test_client_factory):
     client = test_client_factory(app)
     response = client.head("/")
     assert response.text == ""
+
+
+def test_empty_response_100():
+    response = EmptyResponse(status_code=100)
+    assert "content-length" not in response.headers
+
+
+def test_empty_response_200():
+    response = EmptyResponse(status_code=200)
+    assert response.headers["content-length"] == "0"
+
+
+def test_empty_response_204():
+    response = EmptyResponse(status_code=204)
+    assert "content-length" not in response.headers
+
+
+def test_empty_response_204_removing_header():
+    response = EmptyResponse(status_code=204, headers={"content-length": "0"})
+    assert "content-length" not in response.headers
+
+
+def test_empty_response_205():
+    response = EmptyResponse(status_code=205)
+    assert response.headers["content-length"] == "0"
+
+
+def test_empty_response_304():
+    headers = {"content-length": "43"}
+    response = EmptyResponse(status_code=304, headers=headers)
+    assert response.headers["content-length"] == "43"